least expected, breaking under the boats, the swift upshoot of water giving them such a rap that we sometimes thought we had struck a rock.  If one happened to be in the centre of a boil when it broke, it would send them sailing down the stream many times faster than the regular current was travelling, rowing the boat having about as little effect on determining its course as if it was loaded on a flat-car.  The other boat, at times just a few feet away, might be caught in the whirlpools that formed at the edge of the fountains, often opening up suddenly under one side of the boat, causing it to dip until the water poured over the edge, holding it to that one spot in spite of every effort to row away.

Then we would strike peaceful water again, a mile or perhaps, so quiet that a thin covering of clear water over the top of the silt-laden pool beneath, reflecting the tinted walls and the turquoise sky beneath its limpid surface.  Gems of sunlight sparkled on its bosom and scintillated in the ripples left behind by the oars.  When seated with our backs to the strongest light, and when glancing along the top of such a pool instead of into it, the mirror-like surface gave way to a peculiar purplish tone which seemed to cover the pool, so that one would forget it was roily water, and saw only the iridescent beauty of a mountain stream.

The wonderful marble walls—­better known to the miners as the blue limestone walls—­now rose from the water’s edge to a height of eight or nine hundred feet, the surface of its light blue-gray rock being stained to a dark red, or a light red as the case might be, by the iron from the sandstone walls above.  There were a thousand feet of these sandstone layers, red in all its varying hues, capped by the four-hundred foot cross-bedded sandstone wall, breaking sheer, ranging in tone from a soft buff to a golden yellow, with a bloom, or glow, as though illuminated from within.  As we proceeded, another layer could be seen above this, the same limestone and with the same fossils—­an examination of the rock-slides told us—­as the topmost formation at the Grand Canyon.  This was not unlike the cross-bedded sandstone in colour, but lacked its warmth and richness of tint.

A close, examination of the rocks revealed many colours, that figured but little in the grand colour scheme of the canyon as a whole—­the detailed ornamentation of the magnificent rock structure.  A fracture of wall would show the true colour of the rock, beneath the stain; lime crystals studded its surface, like gems glinting in the sunlight; beautifully tinted jasper, resembling the petrified wood found in another part of Arizona, was embedded in the marble wall,—­usually at the point of contact with another formation,—­polished by the sands of the turbid river.

All this told us that we were coming into our own.  Four of the seven notable divisions of rock strata found in the Grand Canyon were now represented in Marble Canyon, and soon the green shale, which underlies the blue limestone, began to crop out by the river as the walls grew higher and the stream cut deeper.